This invention relates to a new process for separating dissolved organic solutes from a water solution, and more particularly, to separating dissolved organic solutes using surfactants as a separating agent.
The use of surfactants, such as soap and synthetic detergents, for dissolving organic compounds, is well known in the art. Particularly, surfactant is applied to hydrophobic organic compounds (chemical substances which have a very low solubility in water) for the purpose either dissolving, emulsifying or dispersing the organic compounds in a water environment.
The ability of surfactants to act as mediators between hydrophobic chemicals and water is related to the surfactant's molecular structure, which contains a hydrophilic part, referred to as the "head", and a hydrophobic part, referred to as the "tail". The particular mechanism utilizes the attractive forces between the surfactant tail and the non-polar organic compounds, and the attractive forces between the surfactant head and the water molecules.
Another particular property of surfactant molecules which may be related to solubilization is aggregation to sub-micron droplets, referred to in the art as micelles. In a water environment, the surfactant molecules constituting the micelle are oriented with the hydrophilic heads towards the water, i.e., outwards, and the hydrophobic tails towards the interior of the micelle. Consequently, the micelle's interior is a hydrophobic micro-environment, capable of retaining organic solutes.
It is also well known to separate surfactant micelles from water by means of an ultrafiltration mechanism. This is typically used when studying the properties of surfactants, or the interaction between surfactants and various solutes. According to this technique, surfactants may be recovered from micellar solutions by passing the solution through an ultrafiltration membrane having a pore size smaller than the size of the micelles.
Additionally, separation of surfactants from water may also be achieved by a mechanism known as foam fractionation. According to this mechanism, liquids containing surfactants may be purified by passing a gas through the liquid, thereby generating a foam. The foam is collected and condensed by means of a mechanical foam breaker. The method is suitable for purifying dilute surfactant solutions, since the concentration of surfactant in the foam is higher than in the original liquid.